1. Field of the Invention
The present invention relates to the field of occlusion/infusion and occlusion/imaging devices and systems.
2. Prior Art
It is increasingly important that a physician or surgeon delivering substances, such as a treatment agent or drug or an image-enhancing agent, is able to efficiently and accurately locate and/or effectively deliver the substance to the desired target tissue. This is particularly true when the concentration of the substance required at the target site cannot be safely or effectively achieved by introduction of the substance to a location remote from the target site or the flow of blood washes away or dilutes the substance too rapidly at the target site. Moreover, the physician may only want to treat the diseased portion of a vessel, organ or tissue and avoid treating the healthy portions.
For example, to achieve localized treatment of tissue, such as tissue in a heart, physicians and surgeons can use catheters and/or guidewires, which may include a balloon(s) and an inflation lumen(s) for use as an occlusive device. Specifically, cardiovascular guide catheters are generally percutaneous devices used to advance through a vasculature of a patient to a region of interest and are devices through which another catheter or device may be inserted. Also, guide catheters commonly have imaging agents injected through their lumen to aid in their positioning and to aid in the visualization of a vascular region of interest. Guide catheters are generally inserted into a proximal percutaneous vascular access site via the inner diameter of a shorter catheter-like device, an introducer. Delivery catheters are generally catheters used to deliver a treatment agent(s) and/or diagnostic device(s) to a region of interest in a vasculature of a patient and typically may be inserted through another catheter (e.g., a guide catheter) while engaged with a guidewire. Delivery catheters may be provided with a lumen(s) and a port(s) to allow the delivery of fluids into the vasculature at the distal end of the delivery catheter and/or at a port(s) along the length of the catheter. Guidewires are generally devices that engage a guide catheter or delivery catheter and are used to guide them through a vasculature of a patient to a region of interest and are typically inserted into the vasculature through another catheter (e.g., the guide catheter, the delivery catheter) or while engaged with another catheter. Typically, the guidewire is advanced into and sub-selects the desired distal vasculature region of interest and then the catheter is advanced over the guidewire to a more distal position. Moreover, balloons may be attached to a delivery catheter, guidewire or guide catheter and an inflation lumen provided to allow balloon inflation and deflation to occlude at will a region of interest in a vasculature.
Also, current OCT (optical coherence tomography) imaging systems are not able to image much more than about 2 mm (typically 1.2 to 1.7 mm) into blood or tissue. Because vessels for which imaging is desired are generally 2 mm in diameter or greater and the imaging device may be in contact with a vessel wall, it is not practical to expect to image the wall of these vessels over their full 360 degree circumference to any vessel wall depth without clearing the blood from the field of view, eliminating the blood's properties impacting imaging depth and/or controlling the catheter's position relative to the vessel wall. Clearing may be accomplished by replacing the blood with a saline or other water based solution (flushing), such as by injecting the solution down the guide catheter.
The frequency of light used in OCT imaging systems is such that its wavelength is short enough for it to interact with individual red blood cells. Use of longer wavelengths to avoid the red blood cell interaction results in a loss of the desired image axial (depth) resolution for vulnerable plaque (VP) detection. The red blood cells have a slightly higher index of refraction than the plasma in which they are suspended. In addition, the red blood cells are shaped like concave lenses, so the OCT light may be re-directed and refocused (diverged) by each red cell it passes through, both to and from the tissue/vessel wall to be imaged. In addition, there are some comparatively minor light energy losses due to absorption and path length changes due to scattering (reflection) by the red cells.
IVUS (intravascular ultrasound) may also be used to image VP's at the desired resolutions, if a high enough ultrasonic frequency is used. In high frequency IVUS systems, the red blood cells are imaged and block/attenuate the ultrasound, degrading the imaging depth. Therefore, such systems will also require a flush for reasons similar to the problems of OCT.
In photodynamic therapy systems, the frequency of the light may be even higher than that used in OCT systems. Thus, to control the amount of light energy that reaches the vessel wall within acceptable limits and to limit the possible damage to the blood cells, flushing is likely to be required.
Flushing of coronary arteries to remove blood from the field of view of the OCT device, very high frequency IVUS device or path of a photodynamic therapy beam is normally accomplished by injecting saline into the vessel to be imaged, either through the guiding catheter or a catheter/sheath that surrounds/incorporates the device. However, a simple flush has quite a few drawbacks and problems:
1. When one effectively flushes, the blood is replaced/extremely diluted with another fluid, usually a saline or other isotonic biocompatible water-based solution, which has little oxygen captured in it. Thus, the time window for imaging is limited by the ischemia consequences of the solution on the heart muscle. The more proximal the flush, the more of the heart muscle is affected. Since imaging is desired in patients usually already suffering from ischemia or previous cardiac muscle ischemic tissue damage, the safe/pain-free (the patient is usually conscious during a catheter based vascular procedure) flushing time period is short.
2. Flow in coronary arteries is laminar and thus tends to flow in streamlines and not mix very rapidly with adjacent streamlines. Thus, injected solutions tend to flow in their own streamlines, leaving some areas of blood flow (some blood streamlines) not completely displaced/replaced or leaving eddies of blood at branch points or areas protected/created by the device's/catheter's/sheath's presence.
3. Most water based flushing solutions have a viscosity that is significantly less than that of blood. Thus, for the incoming flush to create enough pressure in the vessel/vessel path to exceed the blood pressure and thus relatively completely displace the incoming blood, the flow rate of the flush must exceed the normal flow rate of the blood in the vessel. In other words, the resistance to flow in the vessel is lower for the flush than for the blood. So as the flush replaces the flowing blood at the arteriole level, a greater and greater flow rate of the flush is required until a peak flow rate when the flush effectively completely replaces the blood in the artery/arterioles downstream (the flow resistance of the capillaries/arteries is negligible compared to that of the arterioles) and the arterioles are maximally opened in response to tissue ischemia. The volume of flush required can be quite high during extended flushing time periods.
4. In most injection configurations, the required high flush flow rate enters the vessel via a relatively small effective flow cross-section (catheter/sheath exit port(s)), thus the injection velocity is very high. High velocity jets can be damaging to vessel walls. Additionally, the pressures and volumes required are not easily accomplished by manual injections; an injection device is desirable. Injecting a more viscous fluid, like contrast, requires a lower flow rate, but the catheter injection pressure is relatively unchanged due to its higher viscosity. A high viscosity injectate/flush also increases the time it takes to wash out the flush (longer ischemic time after the flushing is stopped) and, of course, contrast is quite expensive relative to normal flushing solutions.
Several methods to deal with these problems have been previously suggested/disclosed:
1. To solve the problems with light, oxygenated blood could be withdrawn from the patient and materials added to the blood to increase the index of refraction of its plasma to that of the red blood cells and then use it as the flush, or this could be done systemically. This would eliminate/effectively minimize the lens effect and the reflection effects of the red blood cells. The remaining absorption effects would be minor. Since the red blood cells are oxygenated, ischemia is not a problem. It has been reported that contrast can be used to make this index of refraction change to the plasma. However, it is likely that it would be very difficult or toxic to make this adjustment systemically. It is likely somewhat easier and faster to perform this with withdrawn blood, but this would require extra equipment/disposables and a time consuming index matching procedure, as well as issues involved with increased blood exposure. The streamlines and injection problems would still be a challenge and hemolysis could be an issue.
2. The imaging can be done very rapidly by decoupling the image data gathering from the image presentation. This limits the time required for flushing and minimizes ischemia. For any given imaging time, the longer the vessel length to be imaged, the less the longitudinal resolution of the image data gathered during a controlled pullback over that length. However, calculations have shown that a significant length of vessel can be imaged in a very short time and still retain longitudinal resolutions that will allow the reliable detection of VPs. The gathered images are recorded and are accessed by the physician at a comprehensible rate/physician controlled manner. If a VP is detected and an increased longitudinal resolution is desired, another pullback of a shorter length can be performed between the pullback positions specified (positions derived from the previous pullback's presentation data). This method provides a means to reduce the ischemic time and the volume of flush solution required, but still requires high flush flow rates and doesn't deal with the problems of streamlines.
3. The distal end of a guide may be modified to deal with the problems of streamlines with guide catheter infusions or flushing. High flow rates, especially since the guide is very proximal, are still required. The guide would have to be designed to be compatible with the imaging or therapy device, and this might make it less compatible with other devices/catheters required to treat a VP or other medical condition.
4. One could image through a fluid filled balloon and eliminate the need for a flush. However, this would still have the ischemia problem, would damage the vessel wall/the VP and likely distort the vessel so its image would be distorted. Imaging a long length of vessel would be very difficult to design a balloon for, because the size of the vessel changes along its length and the balloon inflation pressure would tend to straighten the vessel (damage/distortion). A large balloon could also take a long time to deflate. Also, one would not be able to image effectively through any air trapped in the balloon, due to index of refraction differences. If the balloon were made of a fluoropolymer and/or very thin, then the balloon material wouldn't interfere significantly with the OCT light. Water/water-solution filled perfluorocarbon catheter lumens will not interfere significantly with OCT light.
5. Flushing just proximal to the length of vessel to be imaged will help limit the flush flow rate required, at least where the imaging position is distal in the vessel. This implies that the imaging be done in a catheter or a sheath, and that the imaging device engage a sheath or catheter or a flushing sheath/catheter be inserted along with the imaging device. Since the rotating OCT imaging assembly (imaging core) can be made so small, on the order of 0.004″ diameter, it can be incorporated into a flushing sheath/catheter/other catheter with little size increase. Or, if the imaging device is a guidewire, use a flushing sheath to retain guidewire position after an imaging pullback. Such a system could still be as small or smaller than current IVUS catheters, which can access the vessels of interest.
Also known in the prior art are embolic protection devices, and systems for enabling the insertion and removal of embolic protection devices, for capturing and retaining embolic debris, which may be created during the performance of a therapeutic interventional procedure in a stenosed or occluded region of a blood vessel. Devices and systems of this kind include devices and systems that have a strut assembly or cage, generally self expanding, with a filter element thereover. Devices and systems of this type are disclosed in Published U.S. Patent Applications Nos. 2003/0120303, 2003/0144685, 2003/0212361, 2004/0006361 and 2004/0098032, and are sold under the trademark ACCUNET.